How many factors are there in 9(s + 6t - 3q + 12p)

Molly shared a spool of ribbon with 12 people. each person received 3 feet of ribbon. which equation can she use to find r, the number of feet of ribbon that her spool originally had?

I’m really confused and need your assist me with this question i’ve never been taught

Compute the standard deviation of the following set of data to the nearest whole number. 10, 10, 15, 20, 25